LIDAR optical scanner system

Abstract

An optical scanner system comprises a housing, a detector contained within the housing configured to produce at least two resolvable azimuth fields-of-view relative to a center-axis of the housing, and an external scanner rotating relative to the center-axis of the housing, and switching between at least two elevations relative to a nominal optical axis of a receiver. Motion of the housing azimuthally results in the receiver producing a continuous coverage pattern at multiple elevations produced by the external scanner.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of U.S. Provisional Application No. 61 / 952,803, filed Mar. 13, 2014, which is incorporated herein by reference in its entirety.TECHNICAL FIELD[0002]The disclosure pertains to time-of-flight distance measurement within a volume.BACKGROUND OF THE INVENTION[0003]Various methods are available to mechanically scan an optical beam and an associated receiver field-of-view through a region with the distance measurement based on the calculated round trip delay between the emission of a light pulse in the direction of an object and the subsequent reception of the received signal. The common approach for implementation of the scanning function is the use a mechanical steering mirror driven by an actuator to steer the beam and receiver field of view through the desired region. An alternative approach is to mount the transmitter and receiver on a moving platform such as a multiple-axis gimbals or rotary platform to a...

AI Technical Summary

Benefits of technology

[0011]In the primary embodiment, an optical receiver and transmitter scanner produce fields-of-view and associated beam patterns that are elongated and deviated forward in azimuth to look-ahead slightly from the nominal azimuth scanning position. An external scanner alternately selects or deviates between two or more elevation fields-of-view using an elevation step scan approach. A stepped scan would normally result in gaps in azimuth scan coverage while the receiver is viewing alternating elevation fields; with the gap in coverage governed by the number of elevation deflection segments and the effective dead zone produced as the elevation deviation facet move off a receiver or transmitter aperture. The look-ahead function avoids gaps in coverage by viewing ahead of translation based azimuth coverage using multiple detector elements or by elongating the photon detectors field-of-view in azimuth combined with the use of multiple transmit beams in azimuth to produce individually resolved fields of coverage.

[0015]Using an interleaved deflector and attenuation mask allows a large number of elevation step cycles per each mask rotation relative to the optical housing. The pitch of the interleaved beam deflection regions can be made arbitrarily small with eventual limitation due to degraded image quality due to diffraction effects and scattering and loss at the boarders of the deflection regions. Dependent on the desired azimuth resolution of the scan, required elevation steps and deflector / mask fabrication limitations the required rotation rate of the deflection mask may be equal to the rotation rate of the optical housing to allow the mask to anchored to the base. In this configuration rotation of the optical housing allows the simultaneous scanning of azimuth and elevation, significantly reducing the mechanical complexity of the system.

[0018]For rotational scanner applications, the line scan pattern's fields-of-coverage are tangential to the rotation axis of the system. For applications requiring full 360 degrees azimuth coverage, such as for robotic navigation, continuous rotation of the housing may be desirable. For continuous rotation, placement of the multiple lenses sharing a center oriented detector array offers reduced system complexity or for field update rates higher than the rotation rate of the system. Typical frame update rates of 10 cycles per second dictate housing rotation rates of 600 rpm or greater. For applications requiring less than 180 degrees of coverage, the housing may be nutated side-to-side or using multiple apertures around the perimeter of the housing, sweeps of 90 or 180 degrees can be accommodated.

Problems solved by technology

The primary limitation of mechanically scanning the field of view using a steering mirror is a complex trade-off between power consumption, weight and size of the scanner, efficient use of the optical beam power and stray light rejection.

If the mirror scans a raster pattern over a rectangular field-of-view, the requirement to rapidly accelerate and decelerate the mirror increases power consumption and results in the inefficient use of the scanning time.

An external, multiple-facet, rotating polygon mirror scanner can produce a rapid scanning pattern, but is limited to small transmit and receive apertures.

This configuration allows the scanning of a larger receiver and transmit beam at the expense of a potentially undesirable by-product, the rotation of the relative position of the transmitted beam and the receiver field.

When the exiting beam and receive field needs to pass through the curved optic of a cylindrical window or dome the relationship between the transmitted and received fields rotates, resulting in changing optical distortion and the potential for large amount of transmitter beam scattering into the receiver.

The penalty paid for this design goal is high system complexity and associated cost.

Because of the large number of parallel processing channels, the implementation of the pre-amplification, low resolution A / D and the need for GHz frame word rate dictates a high hardware complexity, limiting the approach to high performance military applications.

This method is also inefficient when combined with low-duty cycle pulsed laser sources since the effective utilization of the receiver occurs for short durations relative to the pulse of the system.

Unfortunately this method can only provide noiseless integration when the noise contribution of the background and thermal leakage currents are negligible relative to the signal shot noise.

This occurs under very dark background conditions that are not achievable under outdoor and bright lighting indoors due to limitations in obtaining a sufficiently narrow optical notch filter spectral width.

Narrow pass optical filters become inefficient and prohibitively expensive as the spectral width is reduced.

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